Electrostatic Discharge (ESD) is a rapid discharge that flows between two objects due to the built-up of static charge. ESD may destroy semiconductor devices because the rapid discharge can produce a relatively large current. Electrostatic discharge (“ESD”) protection structures are needed for integrated circuits. In ESD protection, an ESD circuit is formed near integrated circuit terminals such as input and output pads, and also for power supply terminals. ESD protection circuits may provide a current discharge path so as to reduce the semiconductor failures due to ESD.
In the semiconductor technology, ESD protection devices are generally integrated into integrated circuits. NMOS transistors, Silicon-Controlled Rectifiers (SCRs) and resistor-capacitor (RC) triggered PMOS transistors and/or the like are widely used as ESD protection devices.
SCRs may be conveniently formed by forming parasitic transistors in doped well regions adjacent a terminal, are often used for ESD structures. An SCR can be designed to turn on in response to a voltage applied to the SCR and over a threshold. The turned on SCR may provide a discharge path and then safely conduct ESD stress current through the discharge path. As a result, the internal circuitry coupled to a pad terminal may be protected.
An NPN transistor may be used for ESD protection. The source region of the NPN transistor is typically coupled to a power supply VSS, which is typically grounded. The drain region of the NPN transistor may be coupled to an integrated circuit to be protected. If an electrostatic transient occurs across the drain region and the source region, the NPN transistor is turned on and the ESD current flows from the drain region to the source region, so that the integrated circuit coupled to the drain region is protected.
As semiconductor technologies evolve, advance of submicron semiconductor processes may further reduce the physical size of a semiconductor chip. However, the existing ESD protection mechanisms may not meet the ever-increasing requirements from the semiconductor industry. For example, a RC triggered ESD protection solution may consume a large die area.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.